Electrodeposition of gold on tantalum



Patented Dec. 27, 1949 ANTALU Russell D. Van Gilder, Avalon,Pa.--,Tassignor to the United States of America as represented by theSecretary of War No Drawing. Application May 23, 1945, Serial No.595,381

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) 2 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

My invention relates to the art of electroplating and more particularly,to a method of electrodepositing a strongly adherent, durable andwear-resistant film of gold on tantalum grids for electronic tubes.

The difiiculties encountered in electroplating tantalum with preciousmetals are well known to the art. Such electrodepositions do not bond tothe tantalum and can be stripped with ease.

It is the object of my invention to provide a method by which tantalumgrids for electronic tubes may be electroplated with a very thin butstrongly adherent gold film which will withstand all stresses andstrains which the grid has to undergo while the tube is in operation.

Other objects and advantages of my invention will become apparent fromthe following description.

My invention consists in first heating the tantalum metal preferablywith an induction heating coil in a vacuum of the order of millimetersof mercury to a temperature of approximately 1900 C. After reaching thistemperature the metal is allowed to cool before placing in anelectroplating bath.

In my method of the electrodeposition of gold on tantalum metal theelectroplating bath used comprises gold chlorides and a cyanide salt.Said bath may be prepared by dissolving 2.0 oz. of sodium cyanide in aquantity of lukewarm distilled water, a few ounces less than one U. S.gallon, then adding 0.5 oz. of gold chloride and making up to one gallonof solution. A predetermined portion of said electroplating bath isused, depending upon the size of the tantalum metal to be electroplated.

The pretreated grid of tantalum metal, acting as the cathode, and ananode of gold or graphite are placed in an appropriate amount of saidelectroplating bath and maintained at a temperature of 70 C., whilepassing an electric current through said bath. A very low currentdensity is used, such as .01 ampere per square centimeter and a timelimit of the order of 8 minutes. The plated grid is then washed clean ofsaid electroplating bath solution with distilled water and again placedin a vacuum of approximately 10- millimeters of mercury and heated withan induction heating coil to a temperature of approximately 1100 C.After cooling the plated tantalum grid is ready for use. In followingthe above described method of electrodeposition of gold on said tantalumgrid the weight of gold plated on will be of the order of .3560 gram,when the initial weight of said tantalum grid is of the order of 4.0228grams. This will give a thickness of plated gold of 1 mil on a 5 miltantalum wire.

It is to be understood that variations and modifications may be madewithin the scope of my invention as those skilled in the art willreadily understand.

Having thus described my invention I desire to secure by Letters Patentand claim:

1. The method of electrodepositing a strongly adherent gold film ontantalum grids of electronic tubes comprising heating said tantalum gridin a vacuum to a temperature of approximately 1900" C., allowing saidtantalum grid to cool after it had reached said temperature,electrodepositing a, gold film on said tantalum grid from anelectroplating bath solution consisting essentially of gold chloride,sodium cyanide and water, rinsing the plated metal from saidelectroplating bath solution and heating said plated grid in a vacuum toa temperature of approximately 1100 C.

2. The method of electrodepositing a strongly adherent gold film ontantalum grids of electronic tubes comprising heating said tantalum gridwith an induction heating coil in a vacuum of approximately 10"millimeter of mercury to a temperature of approximately 1900 C.,allowing said tantalum to cool after it had reached said temperature,electrodepositing a gold film on said tantalum grid from anelectroplating bath solution consisting essentially of gold chloride,sodium cyanide and water, rinsing the plated metal from saidelectroplating bath solution and heating said plated grid in a vacuum toa temperature of approximately 1100 C.

RUSSELL D. VAN GILDER.

(References on following page) REFERENCES CITED OTHER REFERENCES Thefollowing references are of record in the Electrodeposition of Metals,by G. Langbein. file of this patent: 1924, pages 510, 511, 512.

Transactions of the American Electrochemical UNHED STATES PATENTSSociety, vol. 23 (1913), pages 32-34. Number Name Date The MetalTantalum, published by Fansteel 6 71 Aylsworth Ju y 1 1904 Metallurgical00., N. Chicago, 111., 1939, pages 1,803,691 Brockway May 5, 19 1 4, 9,2,093,845 c a p 1937 Industrial and Engineering Chemistry, 27 2,107,277Austin Feb. 1 (1935), pages 1166, 1167. 2,116,927 Germer May 10, 19382,133,995 Lukens Oct. 25, 1938 FOREIGN PATENTS Number Country Date 1 5797,485 France Feb. 17, 1936

